Boolean Operators

Computerized searching allows words or phrases expressing different ideas to be combined or contrasted. Choosing which of these search terms to use (and whether to search for these terms in the article text, the abstract, or subject heading) creates a search strategy.

Boolean logical operators such as AND, OR and NOT are applied to a database to create a subset of search results (this subset is called a result set in Boolean math). The search strategy should only display results that contain the specific concept being researched. A search strategy typically eliminates unwanted results, only displaying the information needed to accomplish the research goal.

Both databases and search engines allow Boolean searching, though databases typically offer options for more precise search strategies. Databases and search engines may differ regarding the exact terminology used for certain Boolean operators. Some search engines use the "+" symbol in place of the word "AND" used by databases; or they may employ the "-" symbol where a database uses the word "NOT". The utility of the three most common boolean operators is illustrated below with Venn diagrams.


AND is the operator for "intersection."

Example: reading AND kindergarten

The computer will retrieve only records that mention both reading and kindergarten. The AND operator narrows the number of search results by adding requirements that must be met by the document.

reading kindergarten


OR is the logical operator of "union."

Example: kindergarten OR "grade 1"

The computer will retrieve all records that discuss either kindergarten or "grade 1".   The OR operator widens a search, because the two words would not have to both appear in the same record.   If either word appears, the record is added to the results list.
See the note about phrase search

kindergarten "grade 1"


NOT is the logical operator for "complement" (that is, it displays opposing information).

Example: kindergarten NOT reading

The computer will retrieve those records that discuss kindergarten but not reading.

kindergarten reading


PROXIMITY OPERATORS are the logical operators relating to the positions of words or phrases.

The operators include NEAR (which requires that the second term be within so many words of the first) and WITHIN, which requires that the second word follow after the first word or phrase within a set number of words.

Proximity search is only available in a few databases (Lexis-Nexis and EBSCO, for example). The proximity operators do not appear on the database menus, but must be manually entered using the abbreviated format utilized by the specific database.

EBSCO example: tax w8 reform [ results only appear for those documents where the word tax occurs within one to eight words before the word reform ].

LEXIS-NEXIS example: tax pre/8 reform [ this has the same functionality as the EBSCO example ].

Because the few database vendors who offer proximity operators have not standardized on the terms employed, ask a librarian for assistance if you suspect proximity operators would broaden your search.



Search Strategies

Some databases provide multiple search boxes, allowing a single search to be composed of a mixture of searches. If searching for a specific leader's ethical failure, you can search for articles assigned the subject "ethics" which also include in the article text the name of a specific indivdual.


Keyword Search

Keywords are terms proposed by the author to describe the article. Key words are not a controlled vocabulary like subject headings, granting the author more flexibility in word choice.

For an example of keyword search outside of databases, some social media sites allow authors to index their posts with "hash tags" such as #library research.



Phrase Search

In databases and search engines, words generally need to be enclosed in "quotation marks" to be considered a phrase.  
When quatation marks are not employed, search tools award greater relevance to those results where the document word sequence matches the input phrase: however, most of the results are irrelevant.

Databases provided by EBSCO are set by default to automatically do a Boolean phrase search, so any words in an EBSCO search box are considered a phrase. The automatic phrase search in EBSCO databases can be over-ridden using the "Search Modes" controls immediately under the search boxes. "Find all my search terms" employes the AND operator, while "Find any of my search terms" uses the OR operator.

Searching for long phrases often produces no results. Phrase searches should be restricted to two or three words, unless one is seeking a known quotation.



Subject Search

Subject terms have been assigned to books in the library catalog and to articles in the library databases. Subject terms are a specialized vocabulary for describing concepts in a field of study.

If you know the standard subject terms relevant to your research topic, it is much easier to find highly relevant books and articles.   The opposite is also true: if you cannot determine the assigned term the database uses for a concept, research is incredibly difficult. Most databases have either a subject index which lists the subjects used in the database, or a thesarus which additionally offers links to related subject terms.

A subject index or thesaurus can be challenging to use if you know nothing about a topic. A good place to look for possible subject terms is in the terminology used in your textbook or student guide. If you are struggling to find subject terms, explain your research topic to your instructor or your OCLS librarian, and ask them to help you find at least one relevant subject term.



Text Search

Text search looks for the occurance of search terms through the text of the entire article or book. Because it is searching through dozens or hundreds of pages, it generally produces more results than subject search. However, the results are often irrelevant unless the search term has very restricted usage. Thus, text search is most useful looking for all uses of an obscure word or phrase.

The Google search engine provides only text search, as does the Emerald Insight database provided by OCLS. Both of the search engine and database automatically link words with the AND operator, requiring that all words in the search box be present. Both Google and Emerald Insight also allow the user to surround words with quotation marks to create a phrase. Employ quotation marks to create a phrase search when searching text in order to get the most relevant results.



Earl K. Long Library. The University of New Orleans. (2008) Truncation and wildcard operators. Retrieved from http://library.uno.edu/helpfiles/handouts/LIB-HANDOUT-keyword-boolean.pdf


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